The present invention relates to a sound absorbing structure for an acoustic insulator to perform acoustic insulation or sound absorption, and in particular, to a sound absorbing resin structure with an increased sound absorbing performance, for example, a sound absorbing structure suitable for use as a plate-form part, such as a vehicular body part or interior part.
There are known sound absorbing resin structures implemented for sound absorption by resonance in a hollow or void, or by vibration of a film or membrane. As an exemplary sound absorbing structure by resonance absorption, there is a vehicular resonator, which has a disadvantageously large volume. In addition, the resonator, which is a single body with a single peak of sound absorption, needs to be multiplicated with different volumes to have a sound absorbing structure adapted for sound absorption over a wide frequency range. Such a sound absorbing resin structure with a large volume can, however, be easily molded by a blow molding process, with a rigid structure as well.
On the other hand, a sound absorbing structure using a film, which can be molded in a flat form with ease, tends to have a lower rigidity than the sound absorbing structure by resonance absorption, and needs to be reinforced with an increased thickness or by provision of ribs for a specified rigidity to be secured, in addition to the practical necessity of a back air layer to be provided with measures, such as a partitioning wall, for holding the air layer.
There have been proposed sound absorbing structures using a flat-form member and additionally provided with a function of resonance absorption. In Japanese Patent Application Laid-Open Publication No. 10-18471, there is disclosed a sound absorbing structure in which a perforated flat plate and a corrugate mold plate are superposed on each other, with various volumes of voids formed therebetween. Disclosed in Japanese Patent Application Laid-Open Publication No. 8-301024 is a sound absorbing structure in which a plurality of sheets formed with through holes are laminated with air layers in between.
The sound absorbing structure by resonance absorption can be molded to be rigid with ease, but tends to be large-sized as a whole, and is hardly moldable into a flat form, as a problem. To the contrary, the sound absorbing structure with a sound absorbing film can be molded into a flat form with ease. However, in configuration for adaptation to have an increased rigidity or secured air layers, this structure has commensurate disadvantages in weight or molding feasibility, as a problem.
On the other hand, the sound absorbing structure using a flat-form member and additionally provided with a function of resonance absorption, which has a plurality of laminated plate members, needs adhesion or welding for connection between the plate members after their molding, taking time and cost for production, as a problem.
There thus has been desiderated an improvement for enhancement of sound absorbing performance and strength as well as molding feasibility in the conventional art described, in particular of a sound absorbing structure in terms of a substantially flat one-shot resin mold hollowed with a plurality of separate internal voids having their external openings for their independent external communication on at least one of front and rear sides of the flat mold to effect frequency adjustment or control.
The present invention has been made with such points in view. It therefore is an object of the invention to provide a sound absorbing structure of a resin mold with a plurality of internal voids having openings for external communication at a one-side surface of the mold, which allows for a sound absorbing performance to be achieved over a wide frequency range, a light-weight rigid structure to be obtained in a facilitated manner, a low-cost molding to be performed with ease, and an extensive application covering a wet environment as well as those places difficult of installation of ordinary fiber-make sound absorbing structures.
To achieve the object, an aspect of the invention provides a sound absorbing structure of a resin mold with a plurality of internal voids having openings for external communication at a one-side surface of the mold, wherein a respective internal void has a sectional area parallel to the one-side surface and larger than a corresponding opening and is defined by a surface part formed with the corresponding opening, the respective internal void and the corresponding opening constitute a resonance sound-absorption structure for sound absorption by resonance, and the surface part constitutes a film sound-absorption structure for sound absorption by film.